1. Field of the Invention
This invention relates generally to patterned-media magnetic recording disks, wherein each data bit is stored in a magnetically isolated data island on the disk, and more particularly to a patterned-media disk and disk drive with patterned nondata servo fields for head-positioning.
2. Description of the Related Art
Magnetic recording hard disk drives with patterned magnetic recording media have been proposed to increase the data density. In patterned media, the magnetic recording layer on the disk is patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional continuous media wherein a single “bit” may have multiple magnetic domains separated by domain walls. To produce the required magnetic isolation of the patterned islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced so as to render these spaces essentially nonmagnetic. Alternatively, the patterned media may be fabricated so that that there is no magnetic material in the spaces between the islands. U.S. Pat. Nos. 5,820,769; 5,587,223; and 6,383,598 are representative of various types of patterned media and their methods of fabrication.
Like conventional non-patterned or continuous-media disks, patterned-media disks also have nondata servo regions that are used for read/write head positioning. The nondata servo regions in patterned-media disks contain servo islands or blocks separated by nonmagnetic spaces. The servo blocks are patterned into a position error signal (PES) field that generates a servo readback signal that is demodulated into a PES for positioning the read/write head to the desired data track and maintaining it on track. The proposed pattern of servo blocks and demodulation technique is the conventional amplitude-type quadrature servo pattern that uses four spaced-apart PES fields A-D.
What is needed is a patterned-media magnetic recording disk with servo blocks patterned into a PES field that requires less disk space than the conventional amplitude-type quadrature servo pattern, and a disk drive with a demodulation technique for the servo pattern.